1...That new wire really should be fused/ breakered/ fuse linked
2...You should not leave the factory wiring "as is" in the strict sense. You should pull the bulkhead connector apart, inspect ALL the terminals and repair or replace them. The red/ black former ammeter wires are now in parallel to feed power into the interior, and even though they now share that load, and no longer have to carry the alternator current, they DO need to carry current and still operate. "Voltage drop."
3...You should consider bypassing the ammeter by bolting the red and black together in at the ammeter, in case the ammeter itself is compromised, which happens
4...You should inspect and repair ALL bulkhead connector terminals, AND check for voltage drop most especially in the ignition "run" line, which can at the very least cause over charging (over voltage) problems
